1. Field Of The Invention
This invention relates to vision or non-contact inspection devices and, more particularly, to systems and methods for gauging the thickness and dimensions of a contoured object having complex shapes.
2. Brief Description of The Prior Art
A known method of manufacturing vehicle wheels from metal, such as aluminum, involves hot forging of the metal into a roughly sized and shaped wheel. This forging can include one or more operations in which a portion of an aluminum billet or other pre-form is compressed under extreme temperatures and pressure against particularly shaped forming dies to form the object. The forged wheels are thereafter machined to final dimensions.
It is essential that the forged wheel have sufficient material in all of a variety of critical locations, and be of the proper size and shape, in order to conduct the final machining process for the finished wheel. It is not uncommon during the machining process to discover that there is not enough material on the forged wheel to cut away for the finished wheel. At that point, the wheel must be scrapped, losing not only the material used to make the forged wheel, but also losing the time and expense to transport the forged wheel to the finishing facility and to perform the finishing process on the forged wheel. Furthermore, such defects in one forged wheel are often not an isolated incident and may indicate problems in the forging process, such as with the dies which could result in defects in other wheels produced from the same forge at about the same time.
It is a common practice today in manufacturing forged aluminum wheels to periodically conduct process/product statistical inspections on the forged wheels prior to machining. These inspections are conducted by calipers and other hand held, contact gauging equipment. Therefore, it is necessary that the forged wheels be permitted a sufficient time to cool so that they may be handled by the inspectors. In addition, the present methods of gauging and inspecting these wheels by hand is a tedious task and, as a result, the total turnaround time for gauging a single wheel may be upwards of 3 to 4 hours. If an inspection conducted 3 or 4 hours after the forging discovers a problem with the forging process itself, then several hours worth of production on forged wheels may be scrapped. In addition, conducting spot hand checks on a small sample of the produced wheels cannot readily detect trends which may indicate that a problem is developing in some aspect of the forging process.
It is known in the art to use non-contact means to acquire data about the shape and dimensions of an object. Such non-contact means typically include an illumination source and a light sensitive detector. A light source is used to highlight the overall surface or a select area of the object, or is used as a backlight to obtain a profile. The sensor collects the reflected and/or transmitted light and provides data that is analyzed, compared against a reference, and displayed as a video image or the like.
U.S. Pat. Nos. 4,449,226, 4,798,964 and, 4,679,447 disclose non-contact arrangements for gauging and inspecting the outer surface of wheels. U.S. Pat. No. 4,204,434 discloses a system for ultrasonic testing of welds in wheels. Other non-contact arrangements for inspecting and/or gauging the outer surface and dimensions of objects include U.S. Pat. Nos. 4,674,869, 4,695,163, 4,798,469, 4,803,645, 4,806,777, 4,929,843, 4,982,103, 4,989,984, 4,476,533, 4,576,482, 4,937,445, 5,003,187, 4,964,770, 4,894,551, 4,982,438, 4,872,757 and 4,993,836.
Vehicle wheels, whether the forged preform or the final finished wheel, have critical dimensions both on the inner and outer surfaces and also critical thicknesses that must be maintained in various locations on the wheel. None of the previously known non-contact means for inspecting objects are capable of performing such an inspection on both the inside and outside surfaces of objects such as vehicle wheels, and are also not capable of producing, in a non-destructive manner, cross sectional information on the object under test. Therefore, it is an object of the present invention to provide a system and method for a non-contact video measurement of a generally cylindrical object, such as a vehicle wheel having a plurality of inner and outer curved surfaces, regardless of the temperature of said cylindrical object. It is another object of the present invention to provide a wheel dimensional measurement system which determines the thickness of the wheel along several critical points of the wheel's inner and outer contours in order to determine whether the wheel is within dimensional specifications. It is yet another object of the present invention to provide a system and method for measuring the three dimensional thickness of an object having complexly curved inner surfaces which would not otherwise be reachable with standard, manual measuring devices, or with the light source and sensor arrangements of the prior art visual inspection systems.
It is a further object of the present invention to provide a system and method for gauging wheels which can be incorporated into an overall wheel production process. Furthermore, it is an object of the present invention to provide a real-time wheel measuring system which can inspect a recently forged wheel while the wheel is still hot from the forging process. It is also an object to provide such a wheel inspection system which can detect defects in the most recently forged product, and also detect forging press or die problems, before the defects or equipment problems result in the production of hundreds of out-of-specification wheels which would then have to be scrapped, remelted and reforged.